Set default lead time for product to 0

It is assumed that most business will try to deliver customer as fast as
possible.

Closes #12728

modules/sale/product.py

@@ -33,6 +33,10 @@ class DefaultLeadTime(ModelSQL, ValueMixin):
     __name__ = 'product.configuration.default_lead_time'
     default_lead_time = default_lead_time
 
+    @classmethod
+    def default_default_lead_time(cls, **pattern):
+        return datetime.timedelta(0)
+
 
 class Template(metaclass=PoolMeta):
     __name__ = 'product.template'